Sometimes, instead of errors, bits are erased during the transmission of a message or from a tape or other storage medium. The position, but not the value, of an erased bit is known. We say that a code C can correct r erasures if a message received with no errors and with no more than r erasures can be corrected to a unique codeword that agrees with the message received in all the positions that were not erased. a) Show that a binary code of minimum distance d can correct d − 1 erasures. b) Show that a binary code of minimum distance d can correct t errors and r erasures if d = 2t + r + 1.